Note: Javascript is disabled or is not supported by your browser. For this reason, some items on this page will be unavailable. For more information about this message, please visit this page: About CDC.gov.

Fact Sheet

Introduction

Targeted tuberculosis (TB) testing is used to focus program activities, provider practices, and financial resources on groups at the highest risk for latent tuberculosis infection (LTBI). Once TB disease has been ruled out, those who would benefit from treatment of LTBI should be offered this option regardless of their age.

Every effort should be made to test only those persons at the highest risk, interpret tuberculin skin test (TST) reactions and TB blood test results accurately, and ensure appropriate treatment and completion of the recommended regimen.

Persons at Risk for Developing TB Disease

Generally, persons at high risk for developing TB disease fall into two categories: those who have an increased likelihood of exposure to persons with TB disease, and those with clinical conditions that increase the risk of progression from LTBI to TB disease.

Persons at risk for exposure to persons with TB disease include:

Close contacts of a person with infectious TB disease

Persons who have immigrated from areas of the world with high rates of TB

Children under 4 years of age, or children and adolescents exposed to adults in high-risk categories

Positive IGRA result or a TST Reaction of 15 or more millimeters of induration is considered positive in

Persons with no known risk factors for TB*

* Although skin testing programs should be conducted only among high-risk groups, certain individuals may require TST for employment or school attendance. An approach independent of risk assessment is not recommended by CDC or the American Thoracic Society.

Special Considerations

Questions often arise about the interpretation of TST results in persons with a history of Bacille Calmette-Gurin (BCG) vaccine, HIV infection, and recent contacts to an infectious TB case.

BCG vaccine is currently used in many parts of the world to protect infants and children from severe TB disease, especially TB meningitis. It does not confer lifelong immunity, and its significance in persons receiving the TST causes confusion in the medical and lay community.

History of BCG vaccine is NOT a contraindication for tuberculin skin testing

TST reactivity caused by BCG vaccine generally wanes with time

If more than 5 years have elapsed since administration of BCG vaccine, a positive TST reaction is most likely a result of M. tuberculosis infection

Persons who are HIV infected have a much greater risk for progression to TB disease if they have LTBI.

Individuals with HIV infection may be unable to mount an immune response to the TST and may have false-negative TST results

Usefulness of anergy testing in TST-negative persons who are HIV infected has not been demonstrated

Persons with a positive TST result who are contacts of an individual with infectious TB should be treated regardless of age.

Some TST-negative persons should also be considered for treatment (i.e., young children, immunosuppressed)

Repeat TST in 8–10 weeks if initial test result is negative. A delayed-type hypersensitivity response to tuberculin is detected 2–8 weeks after infection